Method of sealing containers



April 1944= J. E. ROTHROCK ,3

METHOD OF SEALING CONTAINERS Filed April 5, 1940- JOHN E. ROTHROCKINVENTOR.

BY MM (fi. M Q

ATTORNEY.

Patented Apr. 4, 1944 HNETED STATE$ METHOD OF SEALING CONTAINERS 1Claim.

This invention relates to containers for explosives and moreparticularly to ameans of closing plastic containers in a waterproofmanher.

The explosive industry has for many years packed its explosives in papercartridges or paper bags and has supplied blasting caps which areinserted into the explosive to effect priming contact and means ofdetonating the charge. The use of paper cartridges and blasting capspresents certain problems which are definite disadvantages. Wheneverpaper containers of nitro-glycerin explosives are handled, the operatorsin most instances develop severe headaches which are most uncomfortableand reduce their efiiciency. The priming or inserting of blasting capsinto the explosive cartridges is a dangerous job at best, and one whichrequires skill to insure proper priming contact between the blasting capand the explosive. A further disadvantage of the paper cartridges istheir lack of complete waterproofness. This disadvantage of lack ofwaterproofness is becoming more noticeable due to the increase in theuse of ammonium nitrate explosives, since these explosives are verysusceptible to water.

To overcome the various disadvantages of paper cartridges, the use ofmolded plastic cartridges has been developed. The use of plasticcontainers has provided the explosive industry with a means wherebywaterproofness of an explosive has been increased. By packing explosivesin a plastic cartridge and sealing this cartridge in a substantiallywaterproof manner. an assembly is produced in which the operator mayplace reliance. The assembly may be used undera considerable head ofwater and the ex- .plosive therein will generally be in propercondition.

The plastic containers while presenting an ad- Vance in the art, presentthe problem of obtaining a completely waterproof closure. The use ofscrew joints has not been completely successful and often under hghhydrostatic pressures, water will find its way into the explosive. Anadditional disadvantage of the plastic container, is the fact that allof the closures must be fitted into place by a friction. This, ofcourse, is a disadvantage in the explosive art due to safety precautionswhich must be taken. A further disadvantage ls that frictionalpositioning usually takes the form of screwing a cover into a threadedcontainer, and such an operation is diflicult to perform safely on anautomatic machine. This operation is especially difficult to performApplication April 5, 1940, Serial No. 327,991

on a machine such as the Hall packing machine, commonly used in packingexplosives.

It is the object of this invention to provide a means of closing plasticexplosive containers in a simple and-efficient manner which will providea. completely waterproof seal.

A further object of this invention is to provide a closure which is notpositioned by frictional methods.

A further object of this invention is to provide a type closure whichmay be adapted for use on a Hall machine.

A still further object of this invention is to provide a closure whichis more economical than the present friction closing devices.

Other objects will appear hereinafter.

In accordance with this invention, these objects have been accomplishedby providing a sealing disk which fits into an explosive containerprepared from a molded plastic composition. The container may have asmall shoulder cut into the open end thereof for receiving a disk ofmolded plastic. Further, in accordance with this invention, the disk ofmolded plastic, after it has been inserted into the molded plasticcontainer, is adapted due to its, coefficient of expansion to grip theoutside walls of the container and thus give a completely waterproofseal, and thereby form a waterproof assembly.

Described generally, my invention comprises a disk of plastic materialhaving a thermal expansion coefficient sufficiently high so that it maybe sized to fit into a tubular plastic container with between about.0005 and about .003 inch clearance around its periphery when thetemperatures of the disk and the plastic cartridges are substantiallydifferent. For example, my plastic disk, due to its high coemcient ofthermal expansion will, when cooled to F. below the temperature of theplastic cartridge, drop readily onto a shoulder or seat in the open endof a plast c cartridge and upon the two pieces of plastics arriving atthe same temperature, the disk will, due to its thermal expansion, seizethe plastic container in a waterproof manner, and provide a completelywaterproof seal.

Having now indicated in a general way the nature and purpose of thisinvention, there follows a more detailed description of preferred embodLments thereof with reference to the accompanying drawing in which Fig. lis a cross-sectional View of a plastic explosive container havingpositioned in the open end portion thereof a plastic disk which providesthe plastic explosive container with a completely waterproof seal.

Fig. 2 is a cross-sectional view of an individual disk for closingplastic containers.

Fig. 3 is a fragmental view of an alternative means of positioning thedisk into the plastic explosive cartridge.

Fig. 4 is a fragmental view of means of maintaining the disk inposition.

Referring now to the drawing and more particularly to Fig. 1, there isshown an explosive container comprising a tubular casing I made from anon-sparking molding material. The casing l is open at one end, and thisopening contains interior threads 2 designed to receive and mesh withexterior threads on similar explosive cartridges. Exterior threads 3 areshown adejacent the closed end of the plastic explosive casing I Theclosure 4 is reduced to a temperature about 50 F. below the temperatureof the container and .then is positioned on the seat or shoulder 5, andbecause of the high thermal expansion coefficient, firmly grips the sidewalls of the tubular container I when the two materials reach the sametemperature. In order to facilitate positioning the disk, I may slightlytaper the inside walls leading down to the shoulder 5, but thisexpedient is not usually found necessary as the decrease in diameterprovides sufiicient clearance to allow the easy positioning of the diskonto the shoulder.

If found desirable, the closure 4 may be made with concave or convexsurfaces, Fig. 2, depending entirely upon the ease with which moldingmay be accomplished. An advantage of using a convex surface on the topside of the closure 4 is that upon screwing an additional plasticcontainer into the interior threads of the plastic container, a contactis established between the bottom of the additional container and thetop of the convex surfaces which tends to maintain and to forcetheclosure disk into tight contact with the side walls of the container.The edges of the disk may also be slightly convex or rounded to aid informing a line contact between the disk and the container. Line contactsare known to be the easiest method of forming tight joints.

While I have found that the closure of this invention may be placed inthe plastic container on shoulder 5, and that expansion of the disk willgive waterproof contact and p ovide a waterproof container forexplosives, I have also found that an alternative method of obtainingthis type closure, which has certain advantages, is the filling of theshoulder 5 with a mastic material such as, for example, asphalt, wax,cement, heavy grease, resin and like materials, in a manner shown bydotted lines 6, Fig. 3. This type filling prevents any explosive fromlodging on the shoulder 5 and further aids in obtaining a waterproofjoint when the closure 4 is dropped or lightly forced onto the shoulder5. In Fig. 3 the closure 4A is shown by dotted line to indicate itsposition just before entering the recess formed by shoulder 5, and theclosure 4 is also shown by a solid line after it has been positioned.The mastic material which is shown, in place before the closure 4 ispositioned, by dotted line B is forced out of the shoulder when the diskis positioned, and aids in making a waterproof joint which is indicatedby cross-hatching 1.

Although the use of mastic material in some cases is extremelydesirable, I prefer to-use the container without such materials as Ifind that complete waterproof contact may be had by relying entirelyupon the thermal expansion of the closing disk i. The use of the masticmaterial is r advantageous in preventing the explosive from lodging onthe shoulder 5, but actually it does not aid materially in thewaterproofness of the container.

Since there is no reason for opening the con tainers once they arefilled and sealed, I may use a restraining ledge 8, Fig. 4, to aid inpositioning the closure disk 4. This restraining ledge 8 preventsopening or tampering with the container and constitutes a safety featurenot enjoyed by other explosive containers.

The moldable plastic materials which I have found useful in forming theclosure disk of my invention are of the phenol-aldehyde, urea-aldehyde,thiourea-aldehyde, wood flour, or noncombustible filled phenolics, andureas, the lignin fiber or lignocellulose plastics, a fibrous base boundwith thermoplastic lignin resins, polyvinyl compounds, celluloseacetate, cellulose acetate mixed esters, and chlorinated rubber. Thecontrolling feature of the materials which I have found to be adaptablefor closing devices is their thermal expansion coefficient. I have foundthat the moldable materials with a thermal expansion in the order ofabout .00002 in./in./degree C. provide a disk which allows insertioninto a cartridge when there is a temperature differential of about 50 F.and which upon expansion provides a waterproof seal. An additionalfeature which affects the choice of the most desirable plastic for usein this invention is the inherent .characteristic of some of theplastics to cold flow. The phenomenon of cold flow must beconsidered inselecting the plastic to be used, but this phenomenon is not extremelyserious as it is not experienced with the phenolic, urea, or thiourearesins which are the preferable resins and only exists to a slightextent in the vinyl, and acetate resins. The following table shows thethermal expansion of various suitable moldable materials which areadaptable for use in this invention.

TABLE Thermal expansion Coefficient of Moldable plastic gfig gg C.Xl(H

1. 5 2. 0-3. 0 2. 0-6. 0 2. 5-4. 0 Cast phenolics 2.8 Wood flourphenolics 3. 7-7. 5 Styrene 6. 5-7. 5 Vinyl 6. 9

7. 0-9. 0 Casein 8 Hard rubber 8 itrate l2 -l6 Acetate 14 -l6 Throughoutthe specification and claims where I have referred to plastic materials,I mean to use the term plastic in the sense that it is used in themolding plas'tic art. Thus, the term plastic refers to organic molded ormoldable materials which may be, for example, of the thermosetting orthermoplastic type. However, the type explosive to be packed in themoldable plastic container controls the type plastic which is adapt ablefor use. Thus, when nitroglycerin explosives are used, plastics whichnitroglycerin will plasticize cannot be used for the container. Withammonium nitrate explosives, this diificulty is not encountered. Variousmoldable plastics which are known to plasticize with nitroglycerin orother similar explosives, for example, the nitro glycols ornitroethyleneglycol are not contemplated for use as explosive containerswith compositions containing these liquid explosives. They would,however, be suitable and adaptable for use with the ammonium nitratetype explosive. It is to be understood, therefore, that the moldableplastic container and closure which I intend to use will be selectedonly after a consideration of the explosive composition to be packed.

In order to show that a waterproof seal may be obtained with the deviceof this invention, the following specific examples are given.

EXAMPLE 1 A phenol aldehyde cartridge having an inside diameter of about1.25 inches at the shoulder point, see Fig. l, 5, was maintained at roomtemperature in condition for closing. A disk of phenol aldehydecomposition which is slightly larger, about .001 inch, than the insidediameter of the cartridge at the shoulder point when compared at roomtemperature, was cooled at about F., and when equalized was dropped intothe cartridge where it came to rest on the shoulder 5. The two pieceswere then allowed to equalize at room temperature, and, due to theexpansion of the closure disk, a tight waterproof joint was formedbetween the cartridge and disk. In order to test the waterproofness ofthis joint when the assembly had reached room temperature, hydrostaticpressure was applied on the outside of the joint. The joint maintainedits waterproofness under a hydrostatic pressure of 150 feet. Thispressure is well above that encountered in normal bore hole blasting andis comparable with those pressures encountered in shooting deep Wells.

The waterproofness of the device is maintained up to pressures where thecontainendeforms or collapses.

In order to further test the water resistance of the joint, a cartridgewas filled with anhydrous copper sulfate, sealed and placed in a roommaintained at 100 F. and 100% relative humidity for a period of 72hours. During this exposure no moisture vapor passed the joint, sincethe copper sulfate did not develop a blue color, which conclusivelyshows that the seal is vapor tight and gas tight.

EXAMPLE 2 A cartridge formed of a wood flour filled. phenol-aldehydecomposition and having an inside diameter of about 2 inches at theshoulder point, see Fig. l, 5, was maintained at room temperature incondition for closing. A disk of the same composition, which was about.002 inch larger than the inside diameter of the cartridge at theshoulder point when at room temperature, was cooled to about 0 F. andwhen equalized was dropped into the cartridge where it came to rest onthe shoulder 5. The two pieces were then allowed to equalize at roomtemperature, and, due to the expansion of the closure disk, a tightjoint was formed between the cartridge and disk. In order to test thewaterproofness of the cartridge when the assembly has reached roomtemperature, a hydrostatic pressure of 150 feet was applied to the jointfor a period of 20 hours. This joint maintained its waterproofness underthis hydrostatic pressure. This pressure is well above that encounteredin normal bore hole blasting and is comparable with those pressuresencountered in seismic prospecting and deep well shooting.

In the above examples, closed end cartridges have been sealed with adisk but, if desirable, due to economic advantages, the cartridges maybe molded in the form of a tube with both ends open. closure to eachend. The bottom end is usually closed first, the casing filled and thetop closed, but this is not essential since the casing may be filledfrom either end. The disks may be positioned entirely by means of ashoulder or the tubes may be slipped onto a-mandrel for positioning onedisk. The use of a mandrel obviates the need of a shoulder in one end ofthe cartridge, but the use of a shoulder is preferred.

The sealing device of my invention has proved extremely useful inpractical application, because it is simple and easy to insert into aplastic cartridge and because it provides an efficient waterproofclosing. Thus, when plastic cartridges are filled, for example, on aHall machine, and the shuttle makes a turn to bring another row ofcartridges under the tamping rod, I have found that I may positioncooled disks into the open end of the packed plastic cartridges andthereafter allow the temperature to raise by, for example, blowing astream of hot air on the disk, and that this operation provides acompletely waterproof seal for the cartridges. On the next turn of theshuttle, the cartridges are dumped into a receiver and are ready to betaken to the packing house. This method of sealing cartridges is veryfast and very efflcient.

The advantages to be gained by this type disk closure are many, forexample, the closure may be made without using the friction necessitatedby the use of threads. The elimination of friction prevents any hazardwhich might be inherent in screwing a closure into the open end of thecartridge. A further advantage is that the disk when sealed into thecartridge is very difilcult to remove therefrom and this prevents anyattempt to removal when the cartridge is in the field. This provides asafety point which is very much desirable in the explosive industry.

It will be understood that the details-and examples hereinbefore setforth are illustrative only and that the invention as broadly describedand claimed is in no way limited thereby.

What I claim and desire to protect by Letters Patent is:

The method of producing a filled, waterproof, plastic explosivecartridge comprising a container having a shoulder at one end forreceiving a plastic closure member, which method comprises positioning amastic material on said shoulder in such a manner as to eliminate theobstructing effect of said shoulder while the con tainer is being filledwith an explosive, filling that portion of said container below saidshoulder with an explosive, and forcing a closure mem ber, which is at atemperature substantially below that of the container onto saidmastic-filled shoulder, and permitting said closure member to expandinto sealing relationship with said container.

JOHN E. RQ'I'HROCK.

Closing is effected by applying a disk.

